This invention is directed to negative-acting photoimageable compositions which are developable in alkaline aqueous solutions. The invention is particularly applicable to primary photoimaging resists, but is applicable, as well, to compositions that are hardenable so as to form solder masks and the like.
A variety of such photoimageable compositions are described. Essential components of compositions of the type to which the present invention is directed are A) a binder polymer; B) photopolymerizable .alpha.,.beta.-ethylenically unsaturated compound(s), and C) a photoinitiator chemical system. The binder polymer A) has sufficient acid functionality, generally carboxylic acid functionality, that the binder polymer is soluble in alkaline aqueous solution and thereby renders the photoimageable composition developable in alkaline aqueous solutions. The photoimageable compound(s) B) are monomers and/or short chain oligomers, a substantial portion of which are have multiple .alpha.,.beta.-ethylenic unsaturated functionality. Herein, the photoinitiator C), or at least a significant portion of the photoinitiator C) is 9-phenyl acridine or a homologue thereof.